CN115364683B - Method for preparing anti-pollution ultrafiltration membrane by in-situ polyelectrolyte assembly through one-step method - Google Patents

Method for preparing anti-pollution ultrafiltration membrane by in-situ polyelectrolyte assembly through one-step method Download PDF

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CN115364683B
CN115364683B CN202211018390.6A CN202211018390A CN115364683B CN 115364683 B CN115364683 B CN 115364683B CN 202211018390 A CN202211018390 A CN 202211018390A CN 115364683 B CN115364683 B CN 115364683B
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polyelectrolyte
ultrafiltration membrane
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pollution
titanium oxide
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CN115364683A (en
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姜忠义
龙梦影
张润楠
吴洪
杨焯
张诗雨
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Tianjin University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0079—Manufacture of membranes comprising organic and inorganic components
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/30—Polyalkenyl halides
    • B01D71/32—Polyalkenyl halides containing fluorine atoms
    • B01D71/34—Polyvinylidene fluoride
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
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    • Y02A20/124—Water desalination
    • Y02A20/131—Reverse-osmosis

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Abstract

The invention discloses a method for preparing an anti-pollution ultrafiltration membrane by adopting a one-step method to assemble polyelectrolyte in situ. The method mainly comprises the following steps: the film forming polymer, the pore-forming agent and the titanium oxide precursor are dissolved in a solvent to prepare a film casting solution, the coagulating bath is polyelectrolyte aqueous solution with sulfonic acid groups, and the ultrafiltration film is prepared by a non-solvent induced phase inversion method. In the one-step phase conversion process, the precursor is hydrolyzed into hydrophilic titanium oxide which is segregated to a solvent-water interface, and hydrogen bond and coordination interaction are carried out with polyelectrolyte, so that the polyelectrolyte is assembled on the surface of the membrane in situ, and the ultrafiltration membrane is endowed with excellent anti-pollution performance. The invention has the advantages that: the ultrafiltration membrane is prepared by adopting a simple and convenient one-step method to introduce polyelectrolyte in situ, and the film forming and the modification are synchronously realized; the surface properties of the separation membrane can be adjusted by adjusting the addition amount of the titanium oxide precursor and the concentration of the polyelectrolyte in the coagulation bath; the separation membrane has the characteristics of underwater super oleophobic property and super pollution resistance.

Description

Method for preparing anti-pollution ultrafiltration membrane by in-situ polyelectrolyte assembly through one-step method
Technical Field
The invention belongs to a preparation method of an anti-pollution ultrafiltration membrane, and particularly relates to an anti-pollution ultrafiltration membrane prepared by adopting a one-step method to assemble polyelectrolyte in situ.
Background
Novel, efficient, green membrane technology is one of the most competitive water treatment technologies in the 21 st century. The core of the membrane technology is to prepare a selective separation membrane for device integration and application. Compared with the traditional water treatment technologies such as precipitation, distillation, flocculation, adsorption and the like, the membrane technology has the following advantages: (1) the energy consumption is low. The membrane technology mainly realizes separation based on physical properties, and is mostly carried out at normal temperature, and the theoretical energy efficiency is 90% higher than that of rectification. (2) The operation is simple. The membrane separation device is compact, small in volume, flexible in equipment preparation according to the treatment capacity, and beneficial to centralized operation. (3) The application is wide. The membrane technology has little requirement on the type and pollution degree of sewage, can realize liquid separation without adding auxiliary agents, and does not cause secondary pollution. Therefore, the development of the bionic inspired membrane material is oriented to the water resource crisis, has great scientific value and social significance, and can assist the green low-carbon and high-quality development of national economy of China.
Membrane fouling is a bottleneck in the development of membrane technology. The pollutants in the wastewater can block the membrane holes, form a filter cake layer on the surface of the membrane, cause serious membrane pollution, and cause serious problems of sharp flux reduction, increased energy consumption, frequent cleaning, shortened service life and the like. Among them, the oil contaminants are inevitably hydrogen-bonded, van der Waals or hydrophobic interactions on the membrane surface to be difficult to remove from the water purification system. Therefore, the problem of oil pollutants in separation systems is particularly urgent.
It is reported that about 23 water molecules are absorbed per phosphorylcholine molecule, forming a powerful hydration layer, giving the cell membrane perfect antifouling properties. In light of this, polyelectrolytes exhibit great potential in constructing anti-fouling surfaces. Studies have shown that the surfaces of polydiallyl dimethyl ammonium anion coatings having a positive jones-dol viscosity coefficient exhibit self-cleaning properties under water, with oil droplets leaving the surface in 2 seconds. The surface of the polyion film obtained by grafting sodium polyacrylate onto the polyvinylidene fluoride film has ultralow oil adhesion and self-cleaning performance. The surface of the pollution-resistant film is prepared by continuously depositing polyelectrolyte layer by quaternized polycation and sulfonated polyanion. Common methods of surface modification with polyelectrolytes to obtain antifouling properties are surface grafting and coating modification. However, these methods still have some limitations including easy blocking of pores, difficult modification of membrane pores, affected by matrix wettability (difficult modification on hydrophobic or inorganic surfaces due to incompatibility), and complicated steps, time consuming and lack of simplicity and versatility. The surface segregation is a simple in-situ modification method, and charged hydrophilic groups can be enriched on the surface of the membrane in the phase separation process.
Disclosure of Invention
Aiming at the prior art, the invention provides a method for preparing the anti-pollution ultrafiltration membrane by in-situ assembling polyelectrolyte. The polyelectrolyte is introduced in situ by adopting a simple one-step surface segregation method, and the organic-inorganic ultrafiltration hybrid membrane is prepared through hydrogen bond and coordination interaction between the titanium oxide and the polyelectrolyte; the preparation method can adjust the surface property of the selective separation layer by adjusting the addition amount of the titanium oxide precursor and the concentration of polyelectrolyte in the coagulating bath; the separation membrane prepared by the method has the characteristics of underwater super oleophobic property and super pollution resistance.
In order to solve the technical problems, the invention provides a method for preparing an anti-pollution ultrafiltration membrane by adopting a one-step method to assemble polyelectrolyte in situ, which mainly comprises the following steps: dissolving film-forming polymer, pore-forming agent and titanium oxide precursor in solvent, stirring and heating to prepare casting solution; adding polyelectrolyte aqueous solution with sulfonic acid groups into the coagulating bath, and preparing the ultrafiltration membrane by a non-solvent induced phase inversion method. In the phase inversion process, the casting film liquid titanium oxide precursor is hydrolyzed into titanium oxide, the hydrophilic titanium oxide is segregated to the solvent-water interface, and the titanium oxide and polyelectrolyte with sulfonic acid groups are assembled on the film surface in situ through hydrogen bond and coordination interaction; and a firm hydration layer is formed by utilizing the binding force of polyelectrolyte and water molecules, so that the ultrafiltration membrane is endowed with excellent anti-pollution performance.
The invention relates to a method for preparing an anti-pollution ultrafiltration membrane, which comprises the following specific steps:
step one, preparing a casting film liquid: adding a titanium oxide precursor, a film-forming polymer, a pore-forming agent and a solvent into a container according to a certain proportion, wherein the mass ratio of the film-forming polymer to the pore-forming agent to the solvent is 15:8:77, wherein the titanium oxide precursor accounts for 0.68-4.54% of the casting solution by mass; heating and stirring for 8h at 60 ℃, and then standing and defoaming for 12h at 60 ℃ until no obvious bubbles exist for standby;
step two: preparing a coagulating bath: ultrasonically treating a polyelectrolyte aqueous solution with a mass fraction of 1-3% and a sulfonic acid group until the polyelectrolyte aqueous solution is fully dissolved for later use;
step three: in-situ polyelectrolyte is introduced into the ultrafiltration membrane by a one-step phase inversion method: cooling the casting solution prepared in the first step to room temperature, pouring the casting solution on a glass plate, scraping the casting solution into a liquid film with the thickness of 240 mu m, putting the liquid film into the coagulation bath prepared in the second step for 5 minutes at the constant temperature of 25 ℃, solidifying the liquid film, and taking out the solidified film; and (5) taking the solid membrane off the glass plate, and soaking the solid membrane in deionized water for 24 hours to obtain the ultrafiltration membrane.
Wherein: the film-forming polymer is polyvinylidene fluoride (FR 921-2 type), the pore-forming agent is pluronic F127, and the titanium oxide precursor is any one of butyl titanate, titanium tetrachloride and di (2-hydroxy propionic acid) diammonium titanium hydroxide; the solvent is N, N-dimethyl pyrrolidone; the polyelectrolyte with sulfonic acid group is sodium polystyrene sulfonate aqueous solution or polystyrene sulfonic acid aqueous solution.
The titanium oxide precursor accounts for 3.3% of the casting solution by mass; the mass fraction of the polyelectrolyte aqueous solution with sulfonic acid groups is preferably 2%.
The anti-pollution ultrafiltration membrane prepared by the preparation method has the pure water flux of 424-673 Lm -2 h -1 bar -1 . The anti-pollution ultrafiltration membrane is used for intercepting emulsified oil, 0.9g/L of pump oil-water emulsion emulsified by sodium dodecyl sulfate is used as a pollutant, and the surface property and the anti-pollution performance of the anti-pollution ultrafiltration membrane are as follows: the Zeta potential of the surface is-62.1 to-33.6 mV, the contact angle of the underwater oil is 148.2 degrees to 156.1 degrees, the permeability recovery rate (FRR) is 87.6 percent to 99.7 percent, the total permeability reduction rate (DRt) is 0.3 percent to 12.4 percent, and the reversible permeability reduction rate (DRr) is 0.6 percent to 39.3 percent.
Compared with the prior art, the invention has the beneficial effects that:
the preparation method is simple and efficient, polyelectrolyte can be introduced in situ in the one-step phase inversion process, and meanwhile, film formation and modification are realized; compared with amphiphilic segregation agents which are synthesized in multiple steps in other surface segregation methods, the method has the advantages that complex segregation agent synthesis steps and the use of multiple chemical reagents are avoided, and the method is more green and simpler; the ultrafiltration membrane prepared by the method realizes super-strong anti-pollution performance and emulsion separation performance; the chemical composition, the surface Zeta potential and other properties of the ultrafiltration membrane generated in situ can be adjusted by changing the feeding ratio of the coagulating bath, so that the composition structure and the performance of the ultrafiltration membrane can be regulated and controlled.
Drawings
FIG. 1 is a one-step phase inversion process for preparing an anti-fouling ultrafiltration membrane by in situ assembly of a polyelectrolyte.
Fig. 2 shows the permeability recovery rate (FRR), the total permeability decline rate (DRt), and the reversible permeability decline rate (DRr) of the separation membrane. The filter material is 0.9g/L of pump oil water emulsion emulsified by sodium dodecyl sulfate.
Detailed Description
The preparation method of the invention has the design idea that: the polyelectrolyte is introduced on the surface of the membrane to construct a super-strong hydration layer which is used as an effective strategy for preparing the anti-pollution surface. By a one-step surface segregation method, a titanium oxide precursor is added into a casting solution, polyelectrolyte with sulfonic acid groups is added into a coagulating bath, and an organic-inorganic hybrid ultrafiltration membrane with underwater super-oleophylic and antifouling performances is constructed through coordination and hydrogen bond interaction between the titanium oxide and the polyelectrolyte in the phase conversion process. Fig. 1 shows the interaction sites between titania and polyelectrolyte during phase inversion. Anionic SO of polyelectrolyte 3 - Group and titanium oxide precursor hydrolysis Ti (OC) 4 H 9 ) (4-n) n+ (n<4) The cationic groups undergo coordination interactions; hydrogen bonds are created between the sulfur-oxygen bonds of the polyelectrolyte and the hydroxyl groups of the titania. The polyelectrolyte is directly assembled in situ in the non-solvent induced phase separation process, and meanwhile, the film forming and modification are realized, so that the method has the characteristics of simplicity, easiness in operation and excellent film performance.
The method for preparing the anti-pollution ultrafiltration membrane mainly comprises the following steps: dissolving film-forming polymer, pore-forming agent and titanium oxide precursor in solvent, stirring and heating to prepare casting solution; adding polyelectrolyte aqueous solution with sulfonic acid groups into the coagulating bath, and preparing the ultrafiltration membrane by a non-solvent induced phase inversion method. In the phase inversion process, the casting film liquid titanium oxide precursor is hydrolyzed into titanium oxide, the hydrophilic titanium oxide is segregated to the solvent-water interface, and the titanium oxide and polyelectrolyte with sulfonic acid groups are assembled on the film surface in situ through hydrogen bond and coordination interaction; and a firm hydration layer is formed by utilizing the binding force of polyelectrolyte and water molecules, so that the ultrafiltration membrane is endowed with excellent anti-pollution performance. The invention adopts a simple and convenient one-step method, and the ultrafiltration membrane is prepared by introducing polyelectrolyte in situ through hydrogen bond and coordination interaction between titanium oxide and polyelectrolyte, so as to synchronously realize film formation and modification.
In the invention, the film-forming polymer is polyvinylidene fluoride (FR 921-2 type), the pore-forming agent is pluronic F127, and the titanium oxide precursor is any one of butyl titanate, titanium tetrachloride and di (2-hydroxy propionic acid) diammonium titanium hydroxide; the solvent is N, N-dimethyl pyrrolidone; the polyelectrolyte with sulfonic acid group is sodium polystyrene sulfonate aqueous solution or polystyrene sulfonic acid aqueous solution, etc.
The invention will now be further described with reference to the accompanying drawings and specific examples, which are in no way limiting.
Example 1 an anti-fouling ultrafiltration membrane 1 was prepared according to the following procedure.
Step one, preparing a casting film liquid: 1.5g of polyvinylidene fluoride (FR 921-2 type), 0.8g of pluronic F127, 7.7g of N, N-dimethyl pyrrolidone and 0.34g of butyl titanate are added into a round bottom flask, heated and stirred for 8 hours in a water bath at 60 ℃, then kept still at 60 ℃ for defoaming for 12 hours until no obvious bubbles exist, and then a casting solution is prepared.
Step two: preparing a coagulating bath: the method comprises the steps of (1) carrying out ultrasonic treatment on a sodium polystyrene sulfonate aqueous solution with the mass fraction of 2% until the sodium polystyrene sulfonate aqueous solution is fully dissolved to prepare a coagulation bath;
step three: in-situ polyelectrolyte is introduced into the ultrafiltration membrane by a one-step phase inversion method: cooling the casting solution prepared in the first step to room temperature, pouring the casting solution on a glass plate, scraping the casting solution into a liquid film with the thickness of 240 mu m, putting the liquid film into 500mL of the coagulating bath prepared in the second step at the constant temperature of 25 ℃ for 5 minutes, solidifying the liquid film into a film, taking the solid film out of the glass plate, and soaking the solid film in deionized water for 24 hours to obtain the anti-pollution ultrafiltration membrane 1.
FIG. 2 shows that the anti-fouling ultrafiltration membrane 1 prepared in example 1 has anti-fouling fingers FRR, DRt and DRr of 99.5%, 0.5% and 0.6%, respectively, and the filtrate is a 0.9g/L oil-water emulsion of sodium dodecyl sulfate.
The ultrafiltration membrane prepared in example 1 had a specific flux of 560Lm in pure water -2 h -1 bar -1 The method comprises the steps of carrying out a first treatment on the surface of the Zeta potential-54.6 mV; the contact angle of the underwater pump oil is 154.2 degrees.
Example 2 an anti-fouling ultrafiltration membrane 2 was prepared in substantially the same manner as in example 1, except that: in the second step, the polystyrene sodium sulfonate aqueous solution with the mass fraction of 2% is changed into the polystyrene sodium sulfonate aqueous solution with the mass fraction of 1%, and the anti-pollution ultrafiltration membrane 2 is finally obtained.
The anti-pollution indexes FRR, DRt and DRr of the anti-pollution ultrafiltration membrane 2 are 87.6%, 12.4% and 39.3% respectively by using 0.9g/L of pump oil-water emulsion emulsified by sodium dodecyl sulfate as a filter material.
The specific flux of the anti-pollution ultrafiltration membrane 2 prepared in the example 2 in pure water is 673Lm -2 h -1 bar -1 The method comprises the steps of carrying out a first treatment on the surface of the Zeta potential-33.6 mV; the underwater pump oil contact angle is 148.2 degrees.
Example 3 an anti-fouling ultrafiltration membrane 3 was prepared, which was prepared in essentially the same manner as in example 1, except that: in the second step, the polystyrene sodium sulfonate aqueous solution with the mass fraction of 2% is changed into the polystyrene sodium sulfonate aqueous solution with the mass fraction of 3%, and the anti-pollution ultrafiltration membrane 3 is finally obtained.
The filtrate was 0.9g/L of a pump oil water emulsion emulsified with sodium dodecyl sulfate, and the anti-fouling indexes FRR, DRt and DRr of the anti-fouling ultrafiltration membrane 3 were 99.7%, 0.3% and 2.3, respectively.
The specific flux of the anti-pollution ultrafiltration membrane 3 prepared in example 3 in pure water is 424Lm -2 h -1 bar -1 The method comprises the steps of carrying out a first treatment on the surface of the Zeta potential-62.1 mV; the contact angle of the underwater pump oil is 155.2 degrees.
Example 4 an anti-fouling ultrafiltration membrane 4 was prepared in substantially the same manner as in example 1, except that: changing 0.34g of butyl titanate into 0.068g of butyl titanate in the casting solution; finally, the anti-pollution separation membrane 4 is prepared.
The filtrate was 0.9g/L of oil-water emulsion of pump oil emulsified with sodium dodecyl sulfate, and the anti-pollution indexes FRR, DRt and DRr of the anti-pollution ultrafiltration membrane 4 were 89.2%, 10.8% and 2.8%, respectively.
The specific flux of pure water of the anti-pollution ultrafiltration membrane 4 prepared in example 4 is 455Lm -2 h -1 bar -1 The method comprises the steps of carrying out a first treatment on the surface of the Zeta potential-48.0 mV; the contact angle of the underwater pump oil is 149.6 degrees.
Example 5 an anti-fouling ultrafiltration membrane 5 was prepared in substantially the same manner as in example 1, except that: changing 0.34g of butyl titanate into 0.204g of butyl titanate in the casting solution; finally, the anti-pollution separation membrane 5 is prepared.
The filtrate was 0.9g/L of oil-water emulsion of pump oil emulsified with sodium dodecyl sulfate, and the anti-pollution indexes FRR, DRt and DRr of the anti-pollution ultrafiltration membrane 5 were 96.2%, 3.8% and 6.0%, respectively.
The ultrafiltration membrane obtained in example 5 had a specific flux of 543Lm in pure water -2 h -1 bar -1 The method comprises the steps of carrying out a first treatment on the surface of the Zeta potential-51.8 mV; the contact angle of the underwater pump oil is 151.3 degrees.
Example 6 an anti-fouling ultrafiltration membrane 6 was prepared in substantially the same manner as in example 1, except that: changing 0.34g of butyl titanate into 0.476g of butyl titanate in the casting solution; finally, the anti-pollution separation membrane 6 is produced.
The filtrate was 0.9g/L of a pump oil water emulsion emulsified with sodium dodecyl sulfate, and the anti-fouling indexes FRR, DRt and DRr of the anti-fouling ultrafiltration membrane 6 were 97.9%, 2.1% and 1.8%, respectively.
The ultrafiltration membrane obtained in example 6 has a specific flux of 581Lm in pure water -2 h -1 bar -1 The method comprises the steps of carrying out a first treatment on the surface of the Zeta potential-55.9 mV; the underwater pump oil contact angle is 156.1 degrees.
Comparative example 1 comparative separation membrane 1 was prepared as follows:
1.5g of polyvinylidene fluoride (FR 921-2 type), 0.8g of pluronic F127 and 7.7g of N, N-dimethylpyrrolidone are added into a round-bottomed flask, heated and stirred in a water bath at 60 ℃ for 8 hours, and then the mixture is left to stand still for deaeration at 60 ℃ for 12 hours until no obvious bubbles exist, and then a casting solution is prepared. Pouring the prepared casting film liquid to room temperature, scraping the casting film liquid into a liquid film with the thickness of 240 mu m on a glass plate, putting the glass plate into a coagulating bath of 500mL deionized water with the constant temperature of 25 ℃ for 5 minutes, solidifying the casting film liquid into a film, taking the solid film out of the glass plate, and soaking the solid film with the deionized water for 24 hours to obtain the comparative separation film 1.
FIG. 2 shows that the anti-fouling indexes FRR, DRt and DRr of comparative separation membrane 1 were 23.6%, 76.4% and 47%, respectively, and the filtrate was 0.9g/L of a pump oil-water emulsion emulsified with sodium dodecyl sulfate.
The comparative separation membrane 1 had a specific flux of pure water of 512Lm -2 h -1 bar -1 The method comprises the steps of carrying out a first treatment on the surface of the Zeta potential-12.1 mV; the contact angle of the underwater pump oil is 129.2 degrees.
Comparative example 2 comparative separation membrane 2 was prepared as follows:
1.5g of polyvinylidene fluoride (FR 921-2 type), 0.8g of pluronic F127, 7.7g of N, N-dimethylpyrrolidone and 0.34g of butyl titanate are added into a round-bottom flask, heated and stirred for 8 hours in a water bath at 60 ℃, then the mixture is left to stand for deaeration for 12 hours until no obvious bubbles exist, and then a casting solution is prepared. Pouring the prepared casting film liquid to room temperature, scraping the casting film liquid into a liquid film with the thickness of about 240 mu m on a glass plate, putting the liquid film into a coagulating bath with the temperature of 500mL of deionized water at the constant temperature of 25 ℃, curing for 5min to form a film, taking the solid film off the glass plate, and soaking the solid film with the deionized water for 24h to obtain the comparative separation film 2.
FIG. 2 shows that the anti-fouling index of comparative separation membrane 2 is 84.6%, 15.4% and 12.9% FRR, DRt and DRr, respectively, and the filtrate is 0.9g/L of pump oil-water emulsion emulsified with sodium dodecyl sulfate.
The specific flux of pure water of the comparative separation membrane 2 is 443Lm -2 h -1 bar -1 The method comprises the steps of carrying out a first treatment on the surface of the Zeta potential-13.9 mV; the contact angle of the underwater pump oil is 131.5 degrees.
Comparative example 3 comparative separation membrane 3 was prepared as follows:
1.5g of polyvinylidene fluoride (FR 921-2 type), 0.8g of pluronic F127 and 7.7g of N, N-dimethylpyrrolidone are added into a round-bottomed flask, heated and stirred in a water bath at 60 ℃ for 8 hours, and then the mixture is left to stand still for deaeration at 60 ℃ for 12 hours until no obvious bubbles exist, and then a casting solution is prepared. Pouring the prepared casting film liquid to room temperature, scraping the casting film liquid into a liquid film with the thickness of 240 mu m on a glass plate, putting the glass plate into a coagulating bath of 500mL of polystyrene sodium sulfonate aqueous solution with the mass fraction of 2% at the constant temperature of 25 ℃ for 5 minutes, solidifying the casting film liquid into a film, taking the solid film off the glass plate, and soaking the solid film with deionized water for 24 hours to obtain the comparative separation film 3.
FIG. 2 shows that the anti-fouling indexes FRR, DRt and DRr of comparative separation membrane 3 were 57.1%, 42.9% and 31.8%, respectively, and the filtrate was 0.9g/L of a pump oil-water emulsion emulsified with sodium dodecyl sulfate.
The comparative separation membrane 3 had a specific flux of 897Lm in pure water -2 h -1 bar -1 The method comprises the steps of carrying out a first treatment on the surface of the Zeta potential-14.8 mV; the contact angle of the underwater pump oil is 129 degrees.
The surface properties (chargeability and underwater oleophobicity) of the anti-fouling ultrafiltration membranes prepared in examples 1 to 6 of the present invention and the separation membranes prepared in comparative examples 1 to 3 are compared with the anti-fouling properties as shown in table 1.
TABLE 1 analysis of surface Properties and anti-fouling Properties of separation membranes
In conclusion, the preparation method of the anti-pollution ultrafiltration membrane provided by the invention can form a membrane by a one-step method, and is simple and convenient to operate. In the phase inversion process, under the coordination and hydrogen bond interaction between titanium oxide and sodium polystyrene sulfonate, sodium polystyrene sulfonate is introduced to the surface of the membrane in situ, so that firm water and a firm layer are formed on the surface of the membrane, and the ultra-filtration membrane is endowed with excellent anti-pollution performance. The surface structure and the anti-pollution performance of the ultrafiltration membrane can be regulated and controlled by the content of butyl titanate in the membrane casting solution and the concentration of sodium polystyrene sulfonate in the coagulating bath. Since sodium polystyrene sulfonate is a common anionic polyelectrolyte, the Zeta potential of the membrane surface decreases after the interaction of sodium polystyrene sulfonate, which is introduced with negative charges in the coagulation bath, with titanium oxide. As hydrophilic hydroxyl and sulfonic acid groups are introduced, the addition of titanium oxide and sodium polystyrene sulfonate increases the hydrophilicity of the membrane surface, thereby improving the underwater oleophobicity of the membrane surface. The underwater oleophobicity of the membrane surface increases with increasing butyl titanate and sodium polystyrene sulfonate. When the concentration of sodium polystyrene sulfonate is fixed at 2wt%, the water flux increases with the increase of butyl titanate in the casting solution. In the case of the same amount of butyl titanate, the water flux decreases as the concentration of sodium polystyrene sulfonate in the coagulation bath increases. In the invention, the added amount of butyl titanate in the casting solution accounts for 3.3 percent of the mass of the casting solution, and when the concentration of sodium polystyrene sulfonate in the coagulating bath is 2 percent, the prepared ultrafiltration membrane has better comprehensive performance.
Although the invention has been described above with reference to the accompanying drawings, the invention is not limited to the above-described embodiments, which are merely illustrative and not restrictive, and many changes may be made by those skilled in the art without departing from the spirit of the invention, which are all within the protection of the invention.

Claims (6)

1. A method for preparing an anti-pollution ultrafiltration membrane by adopting a one-step method to assemble polyelectrolyte in situ is characterized by mainly comprising the following steps: dissolving film-forming polymer, pore-forming agent and titanium oxide precursor in solvent, stirring and heating to prepare casting solution; adding polyelectrolyte aqueous solution with sulfonic acid groups into the coagulating bath, and preparing an ultrafiltration membrane by a non-solvent induced phase inversion method;
in the phase inversion process, the casting film liquid titanium oxide precursor is hydrolyzed into titanium oxide, the hydrophilic titanium oxide is segregated to the solvent-water interface, and the titanium oxide and polyelectrolyte with sulfonic acid groups are assembled on the film surface in situ through hydrogen bond and coordination interaction; a firm hydration layer is formed by utilizing the binding force of polyelectrolyte and water molecules, so that the ultrafiltration membrane is endowed with excellent anti-pollution performance;
the film-forming polymer is polyvinylidene fluoride, the pore-forming agent is pluronic F127, and the titanium oxide precursor is any one of butyl titanate, titanium tetrachloride and di (2-hydroxy propionic acid) diammonium titanium hydroxide; the solvent is N, N-dimethyl pyrrolidone; the polyelectrolyte with sulfonic acid group is sodium polystyrene sulfonate aqueous solution or polystyrene sulfonic acid aqueous solution.
2. The method for preparing an anti-pollution ultrafiltration membrane according to claim 1, comprising the following specific steps:
step one, preparing a casting film liquid: adding a titanium oxide precursor, a film-forming polymer, a pore-forming agent and a solvent into a container according to a certain proportion, wherein the mass ratio of the film-forming polymer to the pore-forming agent to the solvent is 15:8:77, wherein the titanium oxide precursor accounts for 0.68-4.54% of the mass of the casting solution; heating and stirring for 8h at 60 ℃, and then standing and defoaming for 12h at 60 ℃ until no obvious bubbles exist for standby;
step two: preparing a coagulating bath: ultrasonically treating a polyelectrolyte aqueous solution with a mass fraction of 1% -3% and a sulfonic acid group until the polyelectrolyte aqueous solution is fully dissolved for later use;
step three: in-situ polyelectrolyte is introduced into the ultrafiltration membrane by a one-step phase inversion method: cooling the casting solution prepared in the first step to room temperature, pouring the casting solution on a glass plate, scraping the casting solution into a liquid film with the thickness of 240 mu m, putting the liquid film into the coagulation bath prepared in the second step for 5 minutes at the constant temperature of 25 ℃, solidifying the liquid film, and taking out the solidified film; and (5) taking the solid membrane off the glass plate, and soaking the solid membrane in deionized water for 24 hours to obtain the ultrafiltration membrane.
3. The method for preparing the anti-pollution ultrafiltration membrane according to claim 2, wherein the titanium oxide precursor accounts for 3.3% of the mass of the casting solution.
4. The method for preparing an anti-fouling ultrafiltration membrane according to claim 2, wherein the mass fraction of the polyelectrolyte aqueous solution with sulfonic acid groups is 2%.
5. An anti-pollution ultrafiltration membrane prepared by the method for preparing an anti-pollution ultrafiltration membrane according to any one of claims 1 to 4, wherein the pure water flux is 424-673 Lm -2 h -1 bar -1 。
6. The anti-pollution ultrafiltration membrane used for intercepting emulsified oil according to claim 5, wherein 0.9g/L of pump oil-water emulsion emulsified by sodium dodecyl sulfate is used as a pollutant, and the surface properties and anti-pollution performance of the anti-pollution ultrafiltration membrane are as follows: the Zeta potential of the surface is-62.1 to-33.6 mV, the contact angle of the underwater oil is 148.2 degrees to 156.1 degrees, the permeability recovery rate is 87.6 percent to 99.7 percent, the total permeability reduction rate is 0.3 percent to 12.4 percent, and the reversible permeability reduction rate is 0.6 percent to 39.3 percent.
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EP0302494A2 (en) * 1987-08-04 1989-02-08 Kao Corporation Conjugated polymer-cation exchanger composite membrane and production thereof
WO2015164779A1 (en) * 2014-04-24 2015-10-29 Rensselaer Polytechnic Institute Matrix-free polymer nanocomposites and related products and methods thereof
CN106334447A (en) * 2016-09-28 2017-01-18 东莞市联洲知识产权运营管理有限公司 Anti-pollution composite nano filtering membrane for direct dye waste liquid treatment
CN107441946A (en) * 2017-09-15 2017-12-08 北京工业大学 A kind of method that enzyme induction prepares organic-inorganic hybrid films
CN108939933A (en) * 2018-09-28 2018-12-07 天津工业大学 A kind of preparation method of the amphipathic three block copolymer modified ultrafiltration membrane with pH responsiveness
CN112263919A (en) * 2020-10-27 2021-01-26 盐城海普润科技股份有限公司 Hydrophilic modification method for water treatment separation membrane

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EP0302494A2 (en) * 1987-08-04 1989-02-08 Kao Corporation Conjugated polymer-cation exchanger composite membrane and production thereof
WO2015164779A1 (en) * 2014-04-24 2015-10-29 Rensselaer Polytechnic Institute Matrix-free polymer nanocomposites and related products and methods thereof
CN106334447A (en) * 2016-09-28 2017-01-18 东莞市联洲知识产权运营管理有限公司 Anti-pollution composite nano filtering membrane for direct dye waste liquid treatment
CN107441946A (en) * 2017-09-15 2017-12-08 北京工业大学 A kind of method that enzyme induction prepares organic-inorganic hybrid films
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